Electrolytic cells



April 29, 1947. w. c. GARDINER 2,419,832

ELECTROLYTIC CELLS Filed March 14, 1942 Patented Apr. 29, 1947sLaorRoLY'rro CELLS William C. Gardiner, Niagara Falls, N. Y.,V as-Isignor to lhe Mathieson Alkali Works, Inc., New York, N. Y., acorporation of Virginia Application March 14, 1942. Serial No. 434,751

(o1. coi-231) 2 Claims.

My invention relates to improvements in cells for the production ofmagnesium by electrolysis of magnesium chloride fusions to Whichmagnesium chloride is supplied as a, hydrous salt. Various forms ofcells have been proposed for carrying out this electrolysis. In one suchgenera-l form, the cell is divided to provide an electrolysiscompartment and a feed compartment, anode and cathode elements arearranged in the electrolysis compartment, provision is made forcirculating electrolyte from the feed compartment through theelectrolysis compartment and back to the feed compartment and thehydrous magnesium chloride supplied to the electrolysis is introducedinto the feed compartment Where dehydration is effected and theresulting anhydrous magnesium chloride is incorporated in theelectrolyte. Such dehydration tends to involve decomposition of the saltwith formation oi magnesium oxide and liberation of hydrochloric acidwhich, to the extent that it occurs, imposes operating burdens on thecell and involves a corresponding loss in eillciency. Such decompositioncan be suppressed by maintaining free chlorine present in the region ofdehydration and incorporation of the magnesium chloride into theelectrolyte. Considerable heat is liberated by passage of theelectrolyzing current through the electrolyte. Within limits this heatcan be relied upon to maintain the magnesium chloride fusionconstituting the electrolyte at proper operating temperature. rllheselimits vary with different cells depending more particularly upon thecharacteristics with respect to thermal losses. However, if this sourceof heat is relied upon to maintain the fused electrolyte at operatingtemperature, control of the electrolysis is made dependent upon thethermal losses of the cell. Optimum conditions of production andeniciency are seldom if ever met under these conditions because of thediverse requirements of the cell, thermally and electrically. The heatliberated by the electrolysis can be supplemented externally orinternally, for example by arranging the cell in a heating furnace or bymaking the electrolyte a resistor in an electrical circuit to whichelectrical energy for thus heating the electrolyte is supplied. Theimprovements of my invention, embodied in this general form of cell,provide for independent control of the cell thermally, as well aselectrically, and for suppression of the decomposition to which I havereferred in a simple and advantageous manner.

The improved cell of my invention comprises an electrolysis compartmentand a feed compartment from which fused electrolyte circulates to 2 andthrough the electrolysis compartment and back to the feed compartmentand to which the hydrous salt is supplied, and an anode and cathode inthe electrolysis compartment. In the imy proved cell of my invention,one or more electrodes is arranged in the feed compartment, to beimmersed in the electrolyte during operation, means are provided forpassing an alternating current through these electrodes and theelectrolyte in the feed compartment in Which the electrodes areimmersed, and an electrical connection is established between theseelectrodes and the anode in the electrolysis compartment rendering theelectrodes anodic with respect to the electrolyte. Control of the rateat which energy is thus supplied as alternating current, a control whichdoes not aiect the electrolysis, affords independent thermal control ofthe cell. And, these electrodes being anodic with respect to theelectrolyte, chlorine is liberated at these electrodes which acts tosuppress unwanted decomposition in the feed compartment. Dehydration ofthe hydrous magnesium chloride supplied to the feed compartment, and thefusion of the salt thus supplied, constitute one of the larger thermalburdens on the cell. Thus, in the improved cell of my invention, thesupplementary heat is supplied in a particularly advantageous regionand, coupled with this supply of heat, chlorine acting to suppressdecomposition is introduced into the region in which there is thegreatest tendency toward decomposition. The magnesium liberated by thecurrent flow producing chlorine at the electrodes in the feedcompartment is liberated as part, a relatively small part, of the cellsproduction of magnesium. This unusual combination of functionssimplifies the cell, and

its operation, While accomplishing independent` thermal control of thecell and suppression of decomposition with the advantages I haveindicated.

The accompanying drawing illustrates one form of cell embodying myinvention. This cell is illustrat-ed diagrammatically andconventionally, in sectional elevation with parts broken away in Fig, l,and Figs.` 2 to 5 inclusive illustrate four arrangements of theelectrical circuits used in conjunction with the cell proper illustratedin Fig. 1.

The cell illustrated comprises a steel shell E lined with. refractory l,a refractory partition 8 divides the cell into an electrolysiscompartment 5l and a feed compartment iii. A steel cathode plate ll issupported above the electrolysis compartment by ledges o'n therefractory lining ol the shell 6. An electrical connection |2 to thisplate extends through the top of the cell. A cylindrical steel cathodeelement I 3 is suspended from and electrically connected to the platefor example by welding. A port I4 is provided to permit the escapebeneath the plate |I from Within the element I3 of magnesium liberatedby the electrolysis. A cylindrical steel baille I5 and a cylindricalrefractory liner I 6 serve to trap such magnesium beneath the platewhence it ilows into the metal collecting well II where it collects onthe surface of the magnesium chloride fusion as indicated at |8. Aremovable cover I9 is provided to permit removal of the recoveredmagnesium from the cell. A graphite anode 20 extends into theelectrolysis compartment through an anode compartment 2| and thecylindrical refractory bafile I6. The anode compartment is formed of arefractory floor 22, the upper part of the refractory partition 8, therefractory partition 23 in the form of an incomplete cylinder and acover 24. A passage 25, below the normal electrolyte level, connects theanode compartment with the feed compartment. The anode compartment isalso connected with the electrolysis compartment through the spacewithin the baiiie `|6 around the anode 2li. Chlorine separating in theanode compartment is collected for recovery through connection 2S.Additions to maintain the composition and quantity of the electrolyte,including hydrous magnesium chloride, are supplied to the feedcompartment I 3 through connection 2l. Water vapor and hydrochloric acidgas and any unreacted chlorine liberated in the feed compartment escapethrough connection 23. Connections 21 and 28 open through a cover 29. Apair of graphite electrodes 3D and 3| extend through cover 2S into thefeed compartment to a level below the normal electrolyte level.

The anode 2li and the cathode I3 are' connected to a source of directcurrent of appropriate voltage, 6.5-8.5 volts for example, in theconventional manner as indicated in each of Figs. 2, 3, 4 and 5. Theelectrodes 30 and 3| are connected to a source of alternating current,60 cycle current for example, as illustrated in these figures. Referringfirst to Figs. 2 and 3, the electrodes 3 and 3| are connected across thesecondary of a transformer 32. An individual transformer is withadvantage used with each electrolytic cell. The transformer must beinsulated to withstand the direct current potential above ground of thecell as well as the alternating current potential and the secondarywinding must be designed to carry the direct current as well as thealternating current. The electrodes 30 and 3| are made anodic by anelectrical connection between these electrodes and the anode 20. Asillustrated in Fig. 2, this connection there designated 33 may be aconnection between the anode 20 and the electrode 39 directly and theelectrode 3| through the transformer secondary. As illustrated in Fig. 3this connection there designated 34 may be made to a midpoint of thetransformer secondary. Now referring `tc Figs. 4 and 5, the transformersecondary may be connected across the anode 20 and a single electrode inthe feed compartment, as illustrated in Fig. 5, or across .two or moreelectrodes connected in parallel in the feed compartment as illustratedin Fig. 4. The supplementary heating of the electrolyte effected bypassage of the alternating current through the electrolyte as a resistorcan be controlled, for example, by regulating the immersion of theelectrodes 30 and 3| or by regulating the voltage at which alternatingcurrent is supplied to these electrodes. The rate of chlorineliber-ation in the feed compartment at the electrodes 3|! and 3| can becontrolled by regulating the immersion of these electrodes, and -thisrate of chlorine liberation and the supplementary heating can beindependently controlled by rst establishing the appropriate rate ofchlorine liberation by regulating the immersion of the electrodes andthen establishing the rate of heat supply in the feed compartment byregulating the voltage of the alternating current supply.

In operation, the cell is char-ged with fused electrolyte toapproximately the level indicated in Fig. 1. This electrolyte,previously designated a magnesium chloride fusion, may consist forexample of a fused mixture of chlorides, including magnesium chlorideand one or more of the chlorides of sodium, potassium and calcium. Othersalts such as sodium fluoride may also be included. The proportion ofmagnesium chloride may range from 5% to 50% by weight on the total forexample, This electrolyte is maintained at a temperature of 700-800 C.for example. Magnesium liberated at the cathode collects beneath thecathode plate and flows into the metal collecting well I'I. Chlorineliberated at the anode 2U rises through the baille |6 into the anodecompartment 2|. The electrolyte circulates upwardly through theelectrolysis compartment 9 to the anode compartment 2|, through thepassage 25 from the anode compartmentl to the feed compartment I9 andfrom the feed compartment l0 beneath the partition 8 into theelectrolysis compartment 9. As the electrolysis proceeds, hydrousmagnesium chloride containing froml to 2 moles of water per mole ofmagnesium chloride for example is introduced into the feed compartment,where chlorine is also liberated at electrodes 30 and 3|. The hydrousmagnesium chloride is with advantage introduced in the form of pelletshaving a density approximating that of the electrolyte and containing,for example, about 1% of free carbon. The hydrous salt is dehydrated inthe feed compartment and fused, and its anhydrous component isincorporated into the electrolyte to maintain the concentration ofmagnesium chloride. Thermal requirements of the cell, in excess of theheat liberated in connection with the electrolysis, including the heatrequired for dehydrating and fusing the hydrous magnesium chloride feed,are supplied to the electrolyte in the feed compartment independently ofthe electrolysis as previously described.

I claim:

1. In cells for the production of magnesium by electrolysis of amagnesium chloride fusion to which magnesium chloride is supplied as ahydrous salt, comprising an electrolysis compartment and a feedcompartment from which fused electrolyte circulates to and through theelectrolysis compartment and back to the feed compartment and to whichthe hydrous saltl is supplied and an anode and a cathode in theelectrolysis compartment, the improvement which comprises an electrodein the feed compartment, and means for passing an alternating currentthrough said electrode and the electrolyte in the feed compartmentinwhich it is immersed, said means comprising an electrical connectionbetween said electrode and said anode rendering the electrode anodicwith respect to the electrolyte.

2. In cells for the production of magnesium by electrolysis of amagnesium chloride fusion tov drous salt, comprising an electrolysiscompartment and a feed compartment from which fused electrolytecirculates to and through the electrolysis compartment and back to thefeed compartment and to which the hydr'ous salt is supplied 5 and ananode and a cathode in the electrolysis compartment, the improvementwhich comprises a pair of electrodes in the feed compartment, means forpassing an alternating current through the electrolyte in the feedcompartment between said electrodes, and an electrical connectionbetween said electrodes and said anode rendering the electrodes anodicwith respect to the elecv trolyte.

WILLIAM C. GARDINER.

REFERENCES CITED The following references are of record in the le ofthis patent:

Number UNITED STATES PATENTS Name Date Lyons Mar. 28, 1905 SaklatwallaDec. 1, 1925 Selenyi June 20, 1933 Hulin May 25, 1926 Gue Mar. 10, 1925Blackmore May 18, 1909 Hulin Dec. 27, 1910 D'ow Mar. 29, 1932 MathersFeb. 26, 1924 Phillip Feb, 16, 1937 Barstow Mar. '7, 1933 Mochel Sept.22, 1936

